Cardiac surgery was initially undertaken using highly invasive open procedures. A sternotomy, which is a type of incision in the center of the chest that separates the sternum was typically employed to allow access to the heart. In the past several decades, more and more cardiac operations are performed using intravascular or percutaneous techniques, where access to inner organs or other tissue is gained via a catheter.
Intravascular or percutaneous procedures benefit patients by reducing risk, complications and recovery time. However, the use of intravascular or percutaneous technologies also raises some particular challenges. Medical devices used in intravascular or percutaneous procedures need to be deployed via catheter systems which significantly increase the complexity of the device structure. As well, doctors do not have direct visual contact with the medical devices once the devices are positioned within the body.
One example of where intravascular or percutaneous medical techniques have been employed is in the treatment of a heart disorder called atrial fibrillation. Atrial fibrillation is a disorder in which spurious electrical signals cause an irregular heartbeat. Atrial fibrillation has been treated with open heart methods using a technique known as the “Cox-Maze procedure”. During this procedure, physicians create specific patterns of lesions in the left and right atria to block various paths taken by the spurious electrical signals. Such lesions were originally created using incisions, but are now typically created by ablating the tissue with various techniques including radio-frequency (RF) energy, microwave energy, laser energy, electroporation and cryogenic techniques.
Various catheter-based devices are employed to intravascularly or percutaneously deliver (or sometimes through naturally occurring bodily orifices) various transducers along typically tortuous paths within a body. Recently, catheters employing flexible printed circuits have been successfully deployed in human patients. Flexible printed circuits allow for the economical manufacture of various transducers and their associated circuitry while providing a relatively small compact size that is desirable for percutaneous or intravascular procedures. This is especially important as the desire for increasing numbers of transducers increases. For example, catheters employing several hundreds of transducers have been produced by the applicant using flexible printed techniques.
The present inventors recognized that the stiffness of various portions of the flexible circuit structures may vary based on a number of factors. In this regard, the present inventors recognized that certain portions of the flexible circuit structure, such as the transducers, may be stiffer than other portions of the flexible structure, such as the conductors. The present inventors recognized that the spatial density of circuitry components in the various portions of the flexible circuit structure can affect the stiffness of these portions. For example, the present inventors recognized that portions of the flexible circuit structure corresponding to the transducers may have more conductive material than portions of the flexible circuit structure forming conductive elements connecting the transducers, resulting in the transducer portions being stiffer than the conductive element portions. In percutaneous or intravascular procedures, where the flexible circuit structure is delivered through a catheter, the present inventors recognized that the flexible circuit structure undergoes flexing as it moves through the body, for example, as it follows the natural contours of a bodily path such as a vascular vessel. Due to varying stiffness, the present inventors recognized that it is possible for various conductive elements (e.g., traces) of the flexible circuit to develop a crack due to stress forces imparted to the structure by the flexing. The present inventors also recognized that flexing may occur during a transition from a delivery configuration to an expanded or deployed configuration in some cases. The present inventors recognized that cracks may occur in a boundary region between a portion of the flexible circuit structure having relatively higher stiffness and a portion of the flexible circuit structure having relatively lower stiffness due to stress concentration effects. The present inventors recognized that cracks can lead to an open circuit rendering all or parts of the circuit unusable.
In this regard, the present inventors recognized that there is a need for at least flexible printed circuits that provide circuitry with enhanced durability and robustness suitable to withstand the rigors of percutaneous or intravascular delivery of the flexible printed circuits along tortuous bodily paths.